The present invention relates generally to methods, components and systems for drilling and sealing at subterranean waste sites. These methods, components and systems may also be utilized for other subterranean drilling or sealing procedures. More particularly, embodiments of the present invention relate to the practice of methods for subterranean drilling and sealing where containment of contaminants is needed throughout the drilling and sealing procedures.
Drilling and grouting in hazardous environments, such as at waste sites containing radioactive contaminants (especially those with potential alpha radiation-emitting contaminants) has traditionally been performed remotely, under full containment conditions, or both. These conventional practices may require complex maintenance procedures, may have increased potential for loss of equipment, result in increased secondary waste issues and excessive down time with substantial risk to both the environment and personnel, in addition to having a high cost.
Conventional efforts to provide containment of contamination with respect to drill rig systems during drilling and sealing operations have utilized sacrificial external casings, or sacrificial drill shafts and bits that are left in place in the waste. Such approaches can be costly due to the increased number of necessary components and may undesirably provide infiltration pathways into the buried waste.
U.S. Pat. No. 5,980,446 to Loomis et al., the disclosure of which is incorporated herein by this reference, is directed to a system for stabilizing a subterranean waste site using jet grouting. A thrust block is installed over a subterranean waste site, providing a surface from which drilling into the subterranean waste site can take place with minimal disturbance of the site. Grout monoliths for immobilizing contaminants and filling any voids in the waste site are disclosed and are asserted to aid in containing at many waste sites. However, containment of contaminants during the drilling process is not provided, requiring the practice of additional conventional measures for the use of this technique at radioactive or other highly contaminated sites.
Accordingly, what is needed are systems and processes for drilling and sealing at highly contaminated sites while concurrently maintaining containment of the contaminants. Methods for such containment that enable manned drilling on site and reduce the complexity of systems needed for containment would be advantageous. A process or system that allowed for a drill stem to be inserted into a contaminated site, removed and reinserted at a different location, while maintaining containment would be further advantageous.
The present invention includes systems and methods relating to subterranean drilling while maintaining containment of any contaminants released during the drilling operation. A thrust block installed over a zone of interest provides an overflow space for retaining any contaminants released from the zone of interest and excess sealant returns. A relatively negative air pressure may be maintained in the overflow space by a ventilation system. A number of sealed access ports are placed in the thrust block. The overflow space is sealed from the surrounding environment before drilling with a membrane seal that is punctured by the drill. A flexible sack seal contained in the access port may be connected to a drill shroud prior to drilling, providing containment once the membrane seal is punctured and during drilling. The drill shroud may be adapted to any industry standard drilling rig and includes a connection conduit for connecting to the flexible sack seal and a flexible enclosure between two brackets. As the drill shaft is withdrawn, sealant may be injected to form a sealant column, overlapping sealant columns may create a monolith for immobilizing the contaminants. Upon withdrawal, the sack seal may be closed off and separated, maintaining containment of the overflow space and the drill shroud. The process may be repeated at a number of access ports. Sensors and monitors may be used to verify containment, to monitor sub-thrust block conditions and to examine for leakage throughout the drilling and sealing process.